Sound reproducing device



Aug. 18, 1936. o. cHRls'rENsoN SOUND REPRODUCING DEVICE 2 Sheets-Sheet 1 Filed Sept. 14, 1933 WITNESSES y WM, n 7M. .ww Er vb WC V mm .S 0

ATTORNEYS 2 Sheets-Sheet 2 BY www /Illl/llv fill!! i l ATTORNEY E Aug. 18, 1936. o. cHRlsTENsoN SOUND REPRODUCING DEVICE Filed Sept. 14, 1933 e L m Hnnnunvunnuqunnn l u 2 m 4 n H n l 0 l M 0 .lllm c a. m 7 T w w. 6. l im Q, a. Y M l ---,..w..\\\ .a J SW a. ----mtll- E N 2 h W W M Patented Aug. 18, 1936 UNITED STATES PATENT OFFICE Application September 6 Claims.

This inventionrrelates to a device for producing sound.

An object of the invention is the provision of a device for the reproduction of sound and which (may be employed as a loud speaker, in which a plate is employed formed of two sheets of thin metal having different co-eiiicients of expansion,

" as a. loud speaker unit in which a plate is subjected to changes caused by magnetostriction, -.a cone or other form of diaphragm being rigidly connected to the composite plate by means of a rod secured at the center of the plate so that the receiver becomes an eilicient loud speaker unit.

The composite plate ofthe present receiver vibrates with great force and a cone or other diaphragm connected with the plate may therefore be of -greater size and weight than would be practicable in the case of a dynamic or magnetic speaker. By increasing its area., thickness and rigidity the cone may be made a more eillcient radiator of sound waves.

` A` further object of the invention is the provision of a sound reproducing device in which a plate isformed of a thin sheet of nickel secured finany approved manner to the metal plate having a thermal co-eicient of expansionr which is greater than the co-eflicient of the nickel, so that the nickel plate is maintained under permanent compressive stress which is utilized to increase its magnetic susceptibility and magnetostriction when varyingcurrents are passed through the coil to place the plate for imparting to a cone or diaphragm the vibrations for the reproductions of sound waves, the plate being rigidly secured j`at its opposite ends to a permanent magnet emi ployed inconnection with the loud speaker unit.

This invention will be best understood from a consideration of the following detailed descriptionyin View' of the accompanying drawings forming "a part of the specification; neverthless, it is to be understood that the invention is not conned to the disclosure, being susceptible of such changes and modifications as dene no material departure from the` salient features oi the .inventionas expressed in the appended claims` 14, 1933, Serial No. 689,459

In the drawings:

Figure l is a view in elevation partly in section showing a sound reproducing device constructed in accordance with the principles of my invention,

Figure 2 is a view in elevation of the reproducing unit with the cover in section,

Figure 3 is a transverse vertical section of the unit shown connected to a cone,

Figure 4 is a view in elevation of the unit with 1o the cover in section showing a modified form of the sound-reproducing device and taken along the line 4 4 of Figure 5,

Figure 5 is a section taken at right angles to the section shown in Figure 4, and

Figure 6 is a view in perspective of a permanent magnet showing the blocks for rigidly supporting the opposite ends of a plate.

Referring more particularly to the drawings, I designates a base member formed of insulating material or oi' metal, such as aluminum, and this base member is neatly tted within one end oi.' a cylinder II and connected to said cylinder, as shown at II.

The outer end of the cylinder is provided with 25 a closure I2 which has a centrally disposed opening I3 through which projects a threaded rod I 4. The cover may be formed integrally with the cylinder or may be made separately and connected thereto. A ring magnet I is secured to the base member` i0 and is formed of good magnet steel permanently magnetized across the diameter in line with the pole pieces I'I. This magnet forms a polarizing field for a nickel plate which will be presently described. The magnet I5 is secured to the base member I0 in any approved manner and by means of screws I6. Blocks Il formed of soft steel are likewise secured in position and on. the inner face of the permanent magnet I5 by the screws I6.

A" pair of bars 22 and 23 `extend diametrically of the base member I0 with the bar 22 resting at diametrically opposite points on the magnet I 5. These bars are yconnected together at their ends by means of bolts 24 with the bolts being screwed into threaded perforations in the bar 22. The inner portions of the bars are cut away, as shown at 21, to provide a space for a purpose which will be presently explained.

The metal plate is formed of two thin sheets of metal, such as zinc as indicated at 30,` and a sheet formed of pure nickel, indicated at 3l. These plates', have their adjacent faces, as shown at- 3 2, secured together by means of. soldering. The nickel plate is approximately .005 of an inch viii thickness, 2 inches inv width and 2v2 inches in lengthvwhile the zinc plate is approximately il; of

an inch in thickness, 2 -inches in width and -21/2 inches in length. Pure nickel is employed of dead soft temper. Any appreciable variation from the thickness of the nickel will result in a decrease in sensitivity of the device. zinc plate are tinned on one side with solder and are pressed together with` their tinned surfaces in contact between steel plates which are in turn placedbetween the jaws of a vice. The whole is then heated in any`approved manner until the solder on the surface of the plates is melted. The plates are then pressed tightly together and allowed to cool before removal `from the vice.

Any metal, alloy, or material 'having a linear co4 eillcient of expansion greater than that of nickel may be used to subject the nickel plate to a permanent compressive stress and among such met-'- als having the'largest co-eilicients of expansion are. zinc, aluminum, lead, tin, andV porcelain.

However, lead and tin give results which are far below those obtained from zinc due to their low lmelting points-and low tensile strength. It has been found, however, that aluminum. and especially zinc, give the best results. The zinc plate soldered to the nickel plate, the solder having a melting point of approximately 450 Fr., will subject the nickel to a degree'of compressive stress in which condition its susceptibility and magnetostrictive effects are greatest.

A form 40 made of bakelite or of other rigid insulating' material has wound vthereon coils of.

wire and 46. These coils are provided in the form of a winding of No. 40 B & S gage enamel insulated copper wire. Both coils are wound in the same direction, each coil being simply a continuation of the other. In winding the following procedure is followed: 'I'he assembly is placed in the winding machine and the end of the wire from the spool supply is passed through an opening .in one of the bars 22 or 23 and temporarily sethe winding. This construction has the advantage that both terminals of the winding are brought out at the upper surface of the winding.

One terminal 49 is connected as shown to a. metal 'plate- 50 held in position by the screw 24. The

other ,terminal 5I 'of the winding is connected to 'a metal plate 52 held. in place by the screw 24.

A wire 53 is connected tothe metal plate 50 while a wire 54 is connectedto the plate 52. The wires sa and salare the' lead-in` wires from the instrument. i y

A sheet of insulating material may be wound around the exterior of the coils 45 and 46 and `cemented in position if desired by a suitable lacquer. I e

The plate formed of the thin sheets of zinc and nickel are rigidly secured at their opposite ends to the steel blocks I1 preferably with the nickel surface in, contact with the steel blocks and these blocks are connected to the permanent magnet I5.

The rod I4' has its inner end connected kto the metal plate by means of a head 6| and nuts 62 and 63.

The nickel plate and A diaphragm or cone-which constitutes a vif bratlng element for the reproduction ofa soimd is shown at 65 and this cone is connected to the outer free end 86 of the rod 60. Metal plates 61 and v68 are located upon opposite sides of the diaphragm and are held in place by nuts 69 and 10 threaded onto the rod and into'- close contact with the plates 68 and 6l, respectively.

The purest nickel obtainable annealed to the softest temper is employed in the manufacture of the plate 3| It is to be noted that the removal of harmful impurities from the nickel and annealing it-to the softest temper greatly increases the permeability and magnetostrictive effect and thereby the sensitivity of the speake'runit.

The loudspeaker unit may be connected in the output circuit of a. vacuum tube or coupling transformer or in any other desired way. For best results the magnetizing coils of the speaker unit should be wound to match or slightly exceed the impedance of the' outputy circuit.

This loud speaker unit operating in connection with a cone diaphragm placed'in a baille of standard dimensions gives high qualityreproduction of speech and music in ample volume with power 26 input no greater than that required by standard types ofv speakers .in twide commercial'use.

Owing to its light weight andthe great rigidity with which the vibratory plate .issupported it is especially suited for installation in automobiles 30 and airplanes where severe vibration occurs. Inmy pending application S. N. 611.41171 have stated' that the .telephone receiver described therein operates by changes in the thickness of the ynickel or other magnetostrictive metal or 35 alloy in the composite plate. It is probable that -such changes in thickness of the plate occurs. Changes in thickness of only asmall fraction of a kmillionth of an inch would be sumcient to set up an audible sound wave. With the minute currents necessary to actuate thereceiver it is quite possible itm'ay operate in this way.

Much greater power is required to operate the loud speaker unit and there can be no doubt that in thevpresent construction the composite plate vvibrates in a flexural manner. Nickel contracts in the direction of a magnetic eld and expands perpendicularly in fields of allintensities appar- 1 rently tending to a iixed limit as the magnetizing force is raised to high'values. -The audio currents in the magnetizing coils surrounding the composite plate setup a varying magnetic field and cause proportional magnetostrictive contractions in the thin nickel sheet which flexes the composite plate as a wholewhichin turn transmits its vibrations to the cone diaphragm.

The zinc plate used in constructing the composite plate is of a thickness suiilcient to give the structure a frequency responsive characteristic well up in the audible range. If it is desired to 60 raise still further the natural frequency of vibra tion of the composite plate its zinc component may be increased to double or more its present thickness with but slight decrease resulting in the sensitivity of the loud speaker unit. In all 65 types of telephone receivers in commercial yuse at the present time of which I have any knowledge the diaphragm is actuated by forces from outside of itself. If such diaphragms are lncreased in size beyond la denite limit they be- 70 come extremely ineiliclent.

In the present construction employing the composite plate or diaphragm the plate isactuated by magnetostrictive forces within the plate itself.

If the plate is supplied with enoughpower the 16 e marient tensile stress in theotherwmetal or alloy. Y

tensile stress than by compressive stress.

,alloy Invar has one of the smallest coetcients of magnitude o!` these forces increase as the size of the plate is increased. i

A composite plate to act as the vibratory element in the loud speaker may be constructed so that its magnetostrictive component will be under tensile stress. It has been found that the magnetic susceptibility and magnetostriction effects are increased `in some metals and alloys such as some of the nickel-iron alloys more by The expansion known.

If a sheet of Invar is secured by soldering, `brazing or welding to a sheet oi almost any other metal or alloy it will result in setting up pery plate of the loud speaker unit and of the telephone receiver is critical as to intensity. If the polarizing eld is of too great intensity it reduces the sensitivity of the device. The ring magnet described is designed to supply a. polarizing eld to the plate of an intensity at which its sensitivity is the greatest. If the magnet establishes too strong a field on the plate the polarizing eld may be decreased by inserting a shim of brass or of other non-magnetic material between the pole pieces on the magnet and the composite plate.

The polarizing field may be made adjustable by methods well known in the art such as varying the distance between the permanent magnet and the composite plate by means of an adjusting screw operating on the magnet. speaker unit is connected in the output circuit of a vacuum tube the steady component of the vacuum tube plate current through the coils surrounding the composite plate may establish suilicient magnetism in the plate to maintain the speaker unit at its maximum sensitivity without the aid of a permanent magnet.

The necessary polarizing field may be supplied by means of an auxiliary coil or coils wound around the composite plate and connected with a source of direct current supply. The direct current supply on the other hand may be connected to the coils surrounding the composite plate carrying the audio currents and choke coils of suitable inductance inserted in the direct current supply circuit to prevent the short circuit- .ing of the audio currents.

A plate 3|a which is formed of pure nickel of medium hard temper approximately .02 of an inch thick, 2 inches wide and of such a length that when it is forced down by means of screws malcontraction method and as a vibratory element for use in telephone receivers and loud speakers the pure nickel plate is not as eilicient as the nickel-zinc composite plate.

A thin sheet of nickel, platinite or other high- When the ly magnetostrictive metal or alloy cemented with 'gyptal varnish or otherwise firmly secured to la somewhat thicker sheet of stiff material such as bakelite or hard rubber may be substituted for the composite plate in a telephone receiver. The magnetostrictive metal in this case is not under compressive or tensile stress.

The composite plates may be made in large sizes forV use in loud speakers without cones or other radiating members being attached thereto. These plates as thus constructed are operated as direct radiators of sound. It will be appreciated, however, that suflicient power will have to be applied to operate these larger plates. Soft rubber washers which are unusually thin are inserted under the heads of the screwsV 24 and between the nickel surface of the composite plate which is rmly clamped between the soft rubber washers. Such construction decidedly improves the performance of the device. The soft rubber washers tend also to prevent the vibrations of the plate from being transmitted to the casing or other parts of the assembly.

I claim:-

l. In a sound reproducing device, a plate formed of magnetostrictive metal which is under compressive stress, means coacting with the opposite ends of said plate for maintaining the plate under compressive stress, a coil of wire adjacent the plate adapted to have a current passed therethrough to set up a varying magnetic eld, means for maintaining the plate in a magnetized state, and a diaphragm connected with the plato.

2. In a sound reproducing device, a plate formed of two sheets of metal rigidly secured together, one of the sheets being formed of magnetostrictive metal, one of the sheets being under tensile stress, means coacting with the opposite ends of the plate for maintaining the plate under compressive stress, a coil of wire adjacent the plate adapted to have a current passed therethrough to set up a varying magnetic eld, means for maintaining the plate in a magnetized state, and a diaphragm connected with the plate.

3. In a sound reproducing device, a plate formed of magnetostrictive metal which .is under compressive stress, means coacting with the opposite ends of said plate for maintaining the plate under compressive stress, a coil of wire adjacent the plate adapted to have a current passed therethrough to set up a varying magnetic eld, means for maintaining the plate in a magnetized state, a diaphragm connected with the plate, and means for cushioning the ends of the plate.

4. In a sound reproducing device, a plate formed of two sheets of metal rigidly secured together, one of the sheets being formed of magnetrostrictive metal, one of the sheets being un der compressive stress, the other sheet being under tensile stress, means for securing the opposite ends of the plate in position, a coil of wire adjacent the plate adapted to have a current passed therethrough to set up a varying magnetic eld, means for maintaining the plate in a magnetized state, a diaphragm connected with the plate, and means for cushioning the ends of the plate.

having magnetostrictive metal applied thereto which is` under a compressive stress, means coacting with the opposite ends of the plate for 5. In a sound reproducing device, a plate maintaining the plate under compressive stress,

a coil of wire adjacent the plate adapted to have a current passed therethrough to set up a varying magnetic eld, means for maintaining the plate in a magnetized state, a rod rigidly connected at one end withthe, -center of the plate',v

and a diaphragm connected with the free end of the rod.

6. In a sound reproducing device, a plate formed of two sheets of metal,l one of the sheets being-"formed of magnetostrictive metal, said sheets being secured together at a high temperature and respectively being under compressive andtensile stresses so that a permanent compressive stress and a permanent tensile stress are set up in the plate when the secured sheets have been cooled, a magnet, means for securely 5 OSCAR CHRISTENSON. 

